1. Field of the Invention
This invention relates to circuits for amplifying signals produced by a magnetoresistive element, and more particularly to such circuits for protecting the magnetoresistive element from the occurance of undesirably large currents.
2. Description of the Prior Art
The prior art discloses a magnetic transducer referred to as a magnetoresistive (MR) sensor or head which has been shown to be capable of reading data from a magnetic surface at high linear densities. An MR sensor detects magnetic field signals through the resistance changes of a read element made from a magnetoresistive material. This resistance change is a function of the magnitude and direction of magnetic flux being sensed by the element.
U.S. Pat. No. 4,492,997 discloses an MR head in which the MR element is a two terminal device connected to serve as a portion of the negative feedback resistor of an amplifier circuit so that the amplifier circuit serves both to supply a drive current to the MR element and to amplify the signal derived from the MR element.
U S. Pat. No. 4,660,113 discloses an MR sensor in which the MR element has three terminals with the center terminal connected to ground potential. The outputs from the other two terminals are differentially amplified by a differential amplifier to eliminate external noise signals picked up by the head.
In magnetic recording technology it is continually desired to improve the areal density at which information can be recorded and reliably read. This desire has let to a trend toward greater bit density along a magnetic recording track and a shrinking track width. The greater bit density requires increasingly narrow transducing gaps, increasingly narrow track width, and progressively lower flying height to reliably record and read data.
The MR elements required to meet these requirements are generally small. This factor, along with the lower flying height, leads to an increased chance of damage to the MR element due to currents flowing between the element and its environment. One example is the current caused by intermittent contact between the element and the magnetic recording disk which ca lead to intermittent shorts of the element to the magnetic disk substrate potential. Another example is the current flowing due to galvanic corrosion between the material of the element and the disk magnetic coating or substrate materials in a humid atmosphere.
Commonly assigned U.S. Pat. Nos. 4,706,138 to Jove et al and 4,712,144 to Klaassen disclose circuits for amplifying signals produced by an MR element. These circuits have been shown to operate effectively in amplifying signals produced by the small MR sensors described above.
However, neither the above-mentioned patents nor any other known prior art provide a circuit for protecting the MR element from these damaging currents to the environment of the MR element.